Hydro-dynamic anti-skid braking systems

Abstract

A hydro-dynamic brake system of the type having a volumetric pump circulating brake fluid to a reservoir, and a modulating valve in the output of the pump acting under the control of the brake pedal to constrict the pipeline thereby increasing the pressure at the output of the pump. This pressure is fed to a distributor controlled by a solenoid valve and also receiving an input directly from a master cylinder which is also controlled by the brake pedal. Each wheel has a speed sensor feeding a processing and control circuit which produces an output signal to a solenoid valve which controls various transfer ports of the distributor. The distributor has a series of cylindrical cavities housing pistons which control valves in passages linking the chambers into which each cavity is separated by its piston. These pistons control the flow of brake fluid to the brake actuators so that upon skidding the brakes are released in a rapid but controlled manner, and likewise reapplication of the brakes after skidding is progressive so that there is no "snatching" which might lead to a loss of control.

We claim: 
     
       1. In a hydro-dynamic anti-skid braking system, for motor vehicles, of the type comprising: a master cylinder,   a brake pedal controlling said master cylinder,   a plurality of brake actuators at least one for each wheel of the vehicle,   a reservoir of brake fluid,   a modulating valve controlled by said brake pedal,   a volumetric pump operating to circulate brake fluid from said brake fluid reservoir through said modulating valve controlled by said brake pedal and back to said reservoir,   at least one hydraulic distributor having a solenoid valve and first, second, third and fourth ports,   means connecting said first port to said master cylinder,   means connecting said second port to said brake actuators of at least some of the wheels of said vehicle,   means connecting said third port to the output side of said volumetric pump, and   means connecting said fourth port to said reservoir,   sensor means associated with each of said wheels of said vehicle, operating to detect the speed of said wheels and producing respective output signals,   a processing circuit,   means feeding said output signals from said sensor means to said processing circuit which produces an output signal whenever any of the said wheels of said vehicle is in a skid or incipient skid state,   means feeding said output signal to said solenoid valve of said hydraulic distributor whereby to energise said solenoid valve whenever one of said wheels of said vehicle is in a skid or incipient skid state, whereby to control said distributor to release the brakes when a skid or incipient skid is detected,   the improvement wherein,   said hydraulic distributor comprises a body having first, second and third transfer ports communicating with said solenoid valve which acts to connect said first and second transfer ports together when de-energised and to connect said second and third transfer ports together when energised, said hydraulic distributor body also having:   a first cavity, a first piston in said first cavity separating it into a first chamber communicating with said first and second ports and a second chamber communicating with said third port and with said first transfer port,   a second cavity,   a second piston in said second cavity separating it into first and second chambers,   a first control valve connecting said first chamber of said second cavity with said first chamber of said first cavity, said second chamber of said second cavity communicating with said second chamber of said first cavity,   a third cavity,   a second control valve,   control means,   a third piston in said third cavity separating it into first and second chambers the first communicating with both said first chamber of said second cavity and, via said second control valve with said first port, and the second communicating with said second transfer port via said control means which permit a controlled flow of fluid from said second chamber of said third cavity through said second and third transfer ports to said fourth port when said solenoid valve is energised,   a projection on said first piston serving as a shutter to close communication between said first port and said first chamber of said first cavity when the pressure in said first chamber of said first cavity is lower than the pressure in said second chamber of said first cavity, said first and second control valves acting to prevent the flow of fluid into said first chambers of said second and third cavities respectively when the pressure in these is higher than the pressure in said second chambers of said second and third cavities respectively.   
     
     
       2. The hydro-dynamic braking system of claim 1, wherein said control means comprise: a third control valve,   a fourth cavity in said body of said distributor,   a fourth piston in said fourth cavity separating it into first and second chambers, the first chamber communicating with said second chamber of said third cavity and the second communicating via said third control valve with said second transfer port, said third control valve operating to close such communication when the pressure in said second chamber of said fourth cavity exceeds by a predetermined amount the pressure in said first chamber of said fourth cavity.   
     
     
       3. The hydro-dynamic braking system of claim 1, wherein said control means comprise a fourth cavity having a larger part and a smaller part, a differential piston having a larger part and a smaller part housed in said fourth cavity and separating it into three chambers, a first chamber at the larger end of said cavity, a second chamber of the same diameter as said first chamber at an intermediate position at a shoulder between said larger and smaller parts of said cavity, and a third chamber at said smaller end of said cavity, a passage in said body connecting said third chamber of said fourth cavity with said second transfer port,   a longitudinal passage in said differential piston permitting free communication between said first and third chambers,   a transverse duct of narrow cross section in said differential piston permitting throttled communication between said longitudinal passage and said intermediate chamber;   means at the smaller end of said differential piston for closing said passage leading to said second transfer port,   means connecting said intermediate chamber of said fourth cavity with said second chamber of said third cavity, and   a fourth control valve connecting said intermediate chamber of said fourth cavity with said second transfer port.   
     
     
       4. The hydro-dynamic braking system of claim 2, wherein said fourth piston is provided with a longitudinal hole having a constricted part, which permits communication between said first and second chambers of said fourth cavity. 
     
     
       5. The hydro-dynamic braking system of claim 4, wherein said fourth piston is also provided with a transfer passage having a part extending axially of the piston and a part extending radially of the piston, a passage in the body of said distributor communicating with said radial part of said transfer passage in said fourth piston and leading to said second transfer port.   
     
     
       6. The hydro-dynamic braking system of claim 5, wherein said first chamber of said fourth cavity houses a biasing spring which acts on a thrust element to press a ball over the end of said axial part of said transfer passage in said fourth piston. 
     
     
       7. The hydro-dynamic braking system of claim 3, wherein said fourth control valve is formed by a ball and a light spring which allows the passage of brake fluid from said intermediate chamber of said fourth cavity towards said second transfer port but prevents the flow of brake fluid in the opposite direction.